java接口类型的多态行为练习

首先是接口类

public interface jiekou{  boolean powerOnOff();         //返回当前状态，关还是开  int volumeUp(int increment);  //调大音量  int volumeDown(int decrement);//调低音量  void mute();                  //静音  int setChannel(int channel);  //返回当前频道  int channelUp();              //频道+1  int channelDown();            //频道-1}

然后是TV类

import static java.lang.Math.max;import static java.lang.Math.min;public class TV implements jiekou{                  //创建TV类 public TV(String user, int screensize){            //构造函数   this.user=user;   this.screensize=screensize; } public boolean powerOnOff(){                       //实现接口powerOnOff,在TV类中   power=!power;   System.out.println(user+" "+screensize+" inch TV power "+(power? "on.":"off."));   return power; } public int volumeUp(int increment){                //实现接口调大音量   if(!power){       return 0;   }   volume += increment;   volume = min(volume,MAX_VOLUME);   System.out.println(user+" "+screensize+" inch TV volume level: "+volume);   return volume; } public int volumeDown(int decrement){              //实现接口调小音量   if(!power){      return 0;   }   volume -=decrement;   volume = max(volume,MIN_VOLUME);   System.out.println(user +" "+screensize+" inch TV volume level: "+volume);   return volume; } public void mute(){                                //实现接口静音   if(!power){       return;   }   volume =MIN_VOLUME;   System.out.println(user+" "+screensize +" inch TV volume level: "+volume); }  public int setChannel(int newChannel){            //实现接口返回当前频道   if(!power){       return 0;   }   if(newChannel>=MIN_CHANNEL && newChannel<=MAX_CHANNEL)    channel = newChannel;    System.out.println(user +" "+screensize +" inch TV turned to channel: "+channel);    return channel; }  public int channelUp(){                           //实现接口频道+1   if(!power){    return 0;   }   channel= channel<MAX_CHANNEL ?  ++channel : MIN_CHANNEL;   System.out.println(user +" "+screensize+" inch TV turned to channel: "+ channel);   return channel; } public int channelDown(){                         //实现接口频道-1   if(!power){    return 0;   }   channel = channel>MIN_CHANNEL ? --channel : MAX_CHANNEL;   System.out.println(user +" "+screensize+" inch TV turned to channel: "+ channel);   return channel; } private String user = null; private int screensize = 0; private boolean power = false;  private final int MIN_VOLUME = 0; private final int MAX_VOLUME = 100; private int volume = MIN_VOLUME; private final int MIN_CHANNEL = 0; private final int MAX_CHANNEL = 999; private int channel = MIN_CHANNEL;}

下面是DVD类，它和TV类基本相似，不过少了屏幕大小的参数

import static java.lang.Math.max;import static java.lang.Math.min;public class DVD implements jiekou{                  //创建DVD类 public DVD(String user){                            //构造函数   this.user=user; } public boolean powerOnOff(){                       //实现接口powerOnOff,在DVD类中   power=!power;   System.out.println(user+" DVD Player power "+(power? "on.":"off."));   return power; } public int volumeUp(int increment){                //实现接口调大音量   if(!power){       return 0;   }   volume += increment;   volume = min(volume,MAX_VOLUME);   System.out.println(user+" DVD Player volume level: "+volume);   return volume; } public int volumeDown(int decrement){              //实现接口调小音量   if(!power){      return 0;   }   volume -=decrement;   volume = max(volume,MIN_VOLUME);   System.out.println(user+" DVD Player volume level: "+volume);   return volume; } public void mute(){                                //实现接口静音   if(!power){       return;   }   volume =MIN_VOLUME;   System.out.println(user+" DVD Player volume level: "+volume); }  public int setChannel(int newChannel){            //实现接口返回当前频道   if(!power){       return 0;   }   if(newChannel>=MIN_CHANNEL && newChannel<=MAX_CHANNEL)    channel = newChannel;    System.out.println(user +" DVD Player turned to channel: "+channel);    return channel; }  public int channelUp(){                           //实现接口频道+1   if(!power){    return 0;   }   channel= channel<MAX_CHANNEL ?  ++channel : MIN_CHANNEL;   System.out.println(user +" DVD Player turned to channel: "+ channel);   return channel; } public int channelDown(){                         //实现接口频道-1   if(!power){    return 0;   }   channel = channel>MIN_CHANNEL ? --channel : MAX_CHANNEL;   System.out.println(user +" DVD Player turned to channel: "+ channel);   return channel; } private String user = null; private boolean power = false;  private final int MIN_VOLUME = 0; private final int MAX_VOLUME = 100; private int volume = MIN_VOLUME; private final int MIN_CHANNEL = 0; private final int MAX_CHANNEL = 999; private int channel = MIN_CHANNEL;}

最后是调用的Try类里面的主函数

import static java.lang.Math.random;public class Try{ public static void main(String args[]){   jiekou jie = null;   for(int i=0 ; i<5 ; ++i){    if(random()<0.5)     jie=new TV(random()<0.5 ? "Sony" : "Hitachi",                random()<0.5 ? 46 : 40);    else     jie=new DVD(random()<0.5 ? "Panasonic": "JVC");       jie.powerOnOff();    jie.channelUp();    jie.volumeUp(10);   } }}

下面是结果图

心得体会：感觉和c++差别很小，难度不是太大。